1. Field Of The Invention
The present invention relates generally to casing packers for use in packing an annulus surrounding a string of casing in a well.
2. Description Of The Prior Art
During the construction of an oil or gas well, a casing string is typically placed within the bore hole and cemented in place in the bore hole. This cementing is often performed in multiple stages. It is often desirable to pack off an annulus surrounding a string of casing. This annulus may either be between the casing string and the bore hole, or between two stages of the casing string, with the lower stage being of smaller diameter than an upper stage.
The packers utilized to perform this task may either be individual casing packers which do not have any cementing valve mechanisms associated therewith, or they may be an integral part of a multi-stage cementing tool which includes both a cementing valve apparatus and a packer apparatus which operate in conjunction with each other.
Examples of such multiple stage cementing tools including inflatable packers include U.S. Pat. No. 4,421,165 to Szarka, U.S. Pat. No. 3,948,322 to Baker, and U.S. Pat. No. 3,524,503 to Baker, all assigned to the assignee of the present invention. Such multiple stage cementing tools are also available with compression set packer elements rather than inflatable packer elements.
The present invention is directed to improvements in individual casing packers, i.e., that is casing packers which are not part of a multi-stage cementing tool and which do not have cementing valve apparatus associated therewith as an integral part of the casing packer apparatus. There may of course be other tools in the casing string which may be other casing packers, individual cementing tools, or multi-stage cementing tools. The present invention, however, is directed to an individual casing packer which operates independently of the operation of such other tools which may be present in the string.
With regard to individual casing packers, there are a number of such tools included in the prior art. One such tool marketed by the assignee of the present invention, Halliburton Company, is known as a Halliburton DV Cementing Collar Assembly. This device includes a mechanical compression set packer which is set after a plug is landed on an annular seat within the tool bore and hydraulic pressure is then applied on top of the plug to slide downward an internal sleeve which is connected to an external sleeve which actually compresses the packer element.
The disadvantage of the existing mechanically operated casing packers is that typically they do not have a full opening therethrough because an annular landing surface must be provided for receipt of a plug completely closing the inner bore of the tool in order to operate the tool. Also, removal of the plug may later be necessary after operation of the tool.
Another type of cementing packer which is presently available is an inflatable packer which utilizes a system of spool valves and check valves to control the flow of high pressure fluid into an inflatable packer element. Examples of this type of casing packer include the Halliburton Casing Inflation Packer available from Halliburton Company of Duncan, Okla., and the Tamcap.TM. Inflatable Cementing Packers available from Tam International of Houston, Tex.
The difficulty encountered with existing inflatable casing packers is due to the complex spool valve and check valve mechanisms which are necessary to control the flow of fluid to the inflatable packer.
Thus, there is a need for a simplified design for casing packers which provides increased economy of construction and improved reliability while eliminating the disadvantages mentioned above.